Revisiting the optical interferometry observations of HR 4049

Description

Aims: We present high spatial resolution observations in the mid-infrared of the dusty core of the binary system HR 4049.
Methods: We used the mid-infrared interferometer MIDI/VLTI with 40 m projected baselines. These observations provided two spectrally dispersed visibility curves at a spatial resolution of ~10 mas. Acquisition images and spectra are in addition obtained with a single telescope spatial resolution of ~250 mas.
Results: The MIDI spectra show features due to emission lines (7.9, 8.6 and 11.3 micron) attributed to PAHs. The comparison between ISO and MIDI spectra and dispersed visibility curves allows us to investigate the budget of continuum and PAH emission from distant regions to the inner regions of the compact dusty structure. The flux balance between these different PAH features is different to the one seen in the large beam ISO spectrum, suggesting different contributions at varying locations from the central star for the different PAH species. These features are over-resolved (i.e. their correlated flux is close to zero), placing the bulk of their line forming region at least at 50-70 mas from the central star. The continuum extension is estimated to range between 23 and 27 mas using a Gaussian model, and is very close to the K-band sizes measured with VINCI/VLTI, implying that the emitting regions of the near and mid-IR are similar. The visibilities from the two different baselines do not allow us to constrain the shape of the continuum emitting region but noticeable differences between them suggest that the N band dusty environment is flattened in a direction that coincides with the one suggested by previous polarimetric observations.

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